The invention relates to a thermal electromagnetic radiation detector comprising an absorbent membrane fixed in suspension by thermally insulating support means onto a front face of a substrate comprising at least two electric connection terminals electrically connected to the membrane, the support means comprising at least one support part arranged between the substrate and membrane and having at least one base end and a raised zone.
1. State of the Art
Recent technological progress in silicon microelectronics and achievement of thin films has given a new boost to the technology of thermal radiation detectors comprising an absorbent membrane fixed in suspension on a substrate by thermally insulating support means.
Microelectronics is based on collective processes performed at silicon wafer level, processes which thermal detector technologies can also benefit from in many respects. These collective techniques in fact provide the possibility of achieving matrices of detectors of large complexity, typically matrices of 320×240 detectors, and also of achieving a large number of matrices on a single silicon wafer and therefore of reducing the unit manufacturing cost of the detectors.
The document U.S. Pat. No. 6,094,127 describes a bolometer with three superposed stages, in particular a stage comprising an integrated circuit, a support stage and an absorption stage. The absorption stage and support stage are separated by pillars fixedly secured to the absorption stage. Due to the fact that the support means are arranged between the absorption stage and the stage comprising the integrated circuit, the absorption stage can occupy the whole of the surface of the bolometer, which enables the ratio of the surface of the bolometer sensitive to radiation over the total surface to be increased, thus increasing the efficiency of the bolometer. However, to connect the absorption stage electrically to the support stage, an electric interconnecting part is fitted between the support stage and the absorption stage. This electric interconnecting part is formed by an electrical conduit surrounded by an insulating material. This results in a complex manufacturing process requiring a large number of manufacturing steps and thus presenting high production costs. In particular, the presence of the electric interconnecting part in contact with the absorption stage can have a detrimental effect on the absorption quality and on the sensitivity of the detector. In addition, fabricating an absorption stage having a good flatness is made difficult by the presence of the interconnecting part.
2. Object of the Invention
The object of the invention is to remedy these drawbacks and more particularly to provide a detector having a high ratio of the surface of the bolometer sensitive to radiation over the total surface of the bolometer, while simplifying the manufacturing process thereof.
According to the invention, this object is achieved by the fact that the base end of said support part is fixed to a top part of a conducting pillar having a base fixedly secured to an electric connection terminal, a substantially flat zone of a bottom face of the membrane being directly in contact with the raised zone of the support part.
According to a first particular embodiment of the invention, the support part is formed by an arm having a second end forming the raised zone.
According to a development of the invention, the detector comprises two arms respectively fixed to first and second conducting pillars and each comprising a conducting layer designed to connect the membrane to one of the conducting pillars.
According to a second particular embodiment of the invention, the support part is formed by a bridge having a second base end fixed to a top part of a second pillar, the raised zone being formed by a middle part of the bridge.
According to a development of the invention, the second pillar is conducting and the bridge comprises two conducting layers electrically insulated from one another and designed to electrically connect the membrane respectively to the conducting pillars, the conducting pillars each having a base fixedly secured to an electric connection terminal.
According to a preferred embodiment of the invention, the detector comprises two bridges each comprising a conducting layer designed to connect the membrane to the corresponding conducting pillar.
The raised zone of the support part is preferably formed by a flat segment.
A further object of the invention is to achieve a fabrication process of a detector comprising                deposition of a sacrificial layer on the substrate comprising at least two electric connection terminals,        etching of the sacrificial layer so as to obtain bottom and top flat zones parallel to the substrate, the bottom flat zone covering the electric connection terminals,        deposition, on the sacrificial layer, of a dielectric layer and of a conducting layer designed to form the support part,        etching, in the bottom zone of the sacrificial layer and in the support part, of openings opening out respectively onto the electric connection terminals,        deposition, in said openings, of a conducting layer forming the conducting pillars and etching of the conducting layer forming the conducting pillars,        etching of the dielectric layer and of the conducting layer,        deposition of an additional sacrificial layer on the whole assembly formed by said layers so as to form a common flat surface with the conducting layer forming the support part,        deposition of the membrane on said common flat surface,        removal of the sacrificial layers.        